1. Field of the invention
The present invention relates to a protective diffusion film provided on the light outgoing surface side of a lens film, and more particularly to a protective diffusion film, a process for producing the same, a surface light source device, and a liquid crystal display device, which have been improved in scratch resistance.
2. Background Art
FIG. 5 is a cross-sectional view of a liquid crystal display device 135 provided with a surface light source device 120 which is an edge-type flat light source as an example of a surface light source device using a conventional protective diffusion film.
The surface light source device 120 comprises, for example, a light source 121, a light guide plate 122, reflection film 124, a light diffusive film 125, a lens film 140, and a protective diffusion film 110.
The light guide plate 122 is surface light projection means, and has a light source 121 on its side end and, on its non-light-outgoing surface remote from a light outgoing surface 122a, a dot pattern 123 for diffusing light from the light source 121 and directing the light to a light outgoing direction. The reflection film 124 is provided on the non-light-outgoing surface side of the light guide plate 122, and functions to block off light beams which go out to unnecessary directions and, at the same time, to reflect and return light beams to a predetermined direction.
A lens film 140 is disposed on the light outgoing surface 122a side of the light guide plate 122 through a diffusing plate 125, which diffuses light to conceal the dot pattern 123, in such a manner that the lens film 140 on its prism surface faces the light outgoing surface side.
A protective diffusion film 110 is provided on the light outgoing surface side of the lens film 140. This protective diffusion film: 110 prevents the prism 140a and the liquid crystal display device 133 from coming into direct contact and being scratched with each other, for example, due to vibration in transit. The protective diffusion film 110 also has the effect of slight light diffusion for concealing stripes of the prism 140a in the lens film 140, a spacer (not shown), and the like. To this end, the protective diffusion film has been formed by incorporating, in a dispersed state, organic or inorganic beads as a light diffusing agent into a transparent resin substrate, or by coating an ink containing organic or inorganic beads as a diffusing agent onto a transparent resin substrate.
A transmission liquid crystal display device 133 comprising a liquid crystal layer 130 sandwiched between a lower substrate 132 and an upper substrate 131 is provided on the light outgoing side of the surface light source device 120, and the liquid crystal display device 133 is illuminated from backside by the surface light source device 120.
Since, however, .the protective diffusion film 110 used in the above-described conventional device uses beads as a diffusing agent, the beads disadvantageously scratch the lens film 140 and the liquid crystal display device 133.
Another problem of the conventional device is such that the beads separate from the film and the separated beads enter between the prisms 140a in the lens film 140 and thus cause a change in optical characteristics or create a shadow.
Accordingly, it is an object of the present invention to provide a protective diffusion film, which does not scratch a lens film and a liquid crystal display device, does not become a refuse source or the like, and also has a suitable level of concealment effect, a process for producing the same, a surface light source device, and a liquid crystal display device.
The above object of the present invention can be attained by the following means. In this connection, it should be noted that although, for facilitating the understanding of the present invention, the present invention will be described using reference characters corresponding to embodiments of the present invention, the present invention is not limited to this.
Specifically, the protective diffusion film according to the first aspect of the present invention is a protective diffusion film (10) for use in a surface light source device (20) provided with a lens film (40), wherein said protective diffusion film (10) is provided on a light outgoing surface of the lens film, said protective diffusion film (10) comprising:
a transparent substrate layer (11); and
a protective diffusion layer (13A, 13B) which is provided on the transparent substrate layer in its surface at least on the lens film side, has fine concaves and convexes on its surface, protects members which come into contact with the protective diffusion film, and is light diffusive.
According to a preferred embodiment of the present invention, the protective diffusion film (10) has a haze of 15 to 50.
According to a preferred embodiment of the present invention, the surface of the protective diffusion layer (13A, 13B) has a ten-point mean roughness Rz of 0.5 to 6 xcexcm.
According to a preferred embodiment of the present invention, the number of profile peaks in the concaves and convexes in the protective diffusion layer (13A, 13B) is 2 to 15 as measured under conditions of a reference length of 0.8 mm and a count level of xc2x10.1 xcexcm.
According to a preferred embodiment of the present invention, the number of profile peaks is counted by a Pc1 method.
According to a preferred embodiment of the present invention, the protective diffusion layer (13A, 13B) contains a cured product of an ionizing radiation-curable resin (82).
The protective diffusion film according to the second aspect of the present invention is a protective diffusion film (10) for use in a surface light source device (20) provided with a lens film (40), wherein said protective diffusion film (10) is provided on a light outgoing surface of the lens film, said protective diffusion film comprising:
a transparent substrate layer (11);
a first protective diffusion layer (13B) which is provided on the transparent substrate layer in its surface on the lens film side, has fine concaves and convexes on its surface, protects members which come into contact with the protective diffusion film, and is light diffusive; and
a second protective diffusion layer (13A) which is provided on the transparent substrate layer in its side remote from the first protective diffusion layer, has fine concaves and convexes on its surface, protects members which come into contact with the protective diffusion film, and is light diffusive.
According to a preferred embodiment of the present invention, the protective diffusion film (10) has a haze of 15 to 50.
According to a preferred embodiment of the present invention, the surface of the first protective diffusion layer (13B) and/or the surface of the second protective diffusion layer (13A) has a ten-point mean roughness Rz of 0.5 to 6 xcexcm.
According to a preferred embodiment of the present invention, the number of profile peaks in the concaves and convexes in the first protective diffusion layer (13B) or the second protective diffusion layer is 2 to 15 as measured under conditions of a reference length of 0.8 mm and a count level of xc2x10.1 xcexcm.
According to a preferred embodiment of the present invention, the number of profile peaks in the concaves and convexes in the second protective diffusion layer (13A) or the first protective diffusion layer provided on the side opposite to the first protective diffusion layer (13B) or the second protective diffusion layer is 10 to 40 as measured under conditions of a reference length of 0.8 mm and a count level of xc2x10.1 xcexcm.
According to a preferred embodiment of the present invention, the number of profile peaks is counted by a Pc1 method.
According to a preferred embodiment of the present invention, the protective diffusion layer (13A, 13B) contains a cured product of an ionizing radiation-curable resin (82).
According to the present invention, there is provided a process for producing the protective diffusion film, comprising the steps of:
shaping the ionizing radiation-curable resin into a desired shape by means of a cylinder plate (88) having a mold shape conforming to the shape of said concaves and convexes (step of shaping); and
applying an ionizing radiation to the ionizing radiation-curable resin to form a cured product of the ionizing radiation-curable resin (step of curing).
Further, according to the present invention, there is provided a surface light source device (20) comprising:
a light source (21);
surface light projection means (22) for surface-projecting light, emitted from the light source, from a light projection surface (22a) to a predetermined direction;
a lens film (40) provided on the light projection surface; and
the protective diffusion film (10), according to any one of claims 1 to 13, provided on the light outgoing surface side of the lens film.
Furthermore, according to the present invention, there is provided a liquid crystal display device (35) comprising:
a light source (21);
surface light projection means (22) for surface-projecting light, emitted from the light source, from a light projection surface (22a) to a predetermined direction;
a lens film (40) provided on the light projection surface;
the protective diffusion film (10), according to any one of claims 1 to 13, provided on the light outgoing surface side of the lens film; and
a transmission liquid crystal display device (33) disposed on the light outgoing surface side of the protective diffusion film.